Method of manufacturing hollow rack shaft

Abstract

A workpiece for a hollow rack shaft is a substantially rectangular plate. The opposite two sides of this workpiece are respectively provided with a complementary profile composed of the continuation of a convex portion and a concave portion and when the workpiece is cylindrically formed, the profiles are mutually engaged. As the width of a part the width of which is the largest in the convex portion is larger than that of a part the width of which is the smallest in the concave portion, the two sides are prevented from being detached after engagement. Further, the opposite convex portion and concave portion are mutually caulked and hereby, mutual gap is removed.

What is claimed is:  
     
       1. A method of manufacturing a hollow rack shaft comprising: 
       providing a substantially rectangular plate;  
       forming complementary profiles composed of the continuation of a convex portion and a concave portion along opposing long sides of said plate so that a first portion of said plate is narrower than a second portion of said plate;  
       forming said plate into a channel;  
       forming a rack in said first portion; and  
       forming said channel into a hollow shaft so that the complementary profiles on said long sides engage each other.  
     
     
       2. A method of manufacturing a hollow rack shaft according to  claim 1 , further comprising caulking said convex portion and/or said concave portion of said joined sides to deform a boundary between adjacent convex and concave portions. 
     
     
       3. The method of  claim 1 , wherein a portion of the hollow shaft proximate to said rack has a D-shaped cross section and a portion distal from the said rack has a O-shaped cross section. 
     
     
       4. The method of  claim 1 , wherein providing the rectangular plate comprises: 
       providing a first plate;  
       providing a second plate; and  
       joining the first and second plates in an edge-to-edge fashion so that the first plate corresponds to the first portion of the rectangular plate and the second plate corresponds to the second portion of the rectangular plate.  
     
     
       5. The method of  claim 4 , wherein joining the first and second plates comprises welding said first and second plates together. 
     
     
       6. The method of  claim 4 , wherein the first plate is thicker than said second plate. 
     
     
       7. The method of  claim 4 , wherein the first and second plates are of different materials. 
     
     
       8. The method of  claim 1 , wherein providing the rectangular plate comprises: 
       providing a first plate;  
       providing a second plate defining an aperture; and  
       deposing the first plate in the aperture so that said first plate is parallel to said second plate.  
     
     
       9. The method of  claim 8 , wherein joining the first and second plates comprises welding said first and second plates together. 
     
     
       10. The method of  claim 9  wherein the first plate is thicker than said second plate. 
     
     
       11. The method of  claim 9  wherein the first and second plates are of different materials. 
     
     
       12. A method of manufacturing a hollow rack shaft comprising: 
       providing a rectangular plate;  
       forming a row of rack teeth in a part of said substantially rectangular plate; and  
       cylindrically deforming said rectangular plate by bending it so that the parallel two sides are joined,  
       wherein said rectangular plate comprises a first plate joined to a second plate and said rack teeth are formed in at least a portion of said first plate.  
     
     
       13. A method of manufacturing a hollow rack shaft according to  claim 1 , wherein: 
       said first plate is thicker than said second plate.  
     
     
       14. A method of manufacturing a hollow rack shaft according to  claim 1 , wherein: 
       said first plate is made of material more satisfactory in hardenability than that of said second plate.  
     
     
       15. A method of manufacturing a hollow rack shaft, comprising: 
       providing a plate with a first area having a narrower width than a second area;  
       forming in said first area, a row of rack teeth;  
       deforming said plate to form a hollow shaft having a semi-cylindrical cross section in said first area and a cylindrical cross section in said second area so that said second area has a diameter that is different from the diameter of the semi-cylindrical part in said first area.